LOC semiconductor assembled with room temperature adhesive

ABSTRACT

A semiconductor device assembly has a lead frame and a semiconductor device configured to be attached to each other. An adhesive is applied at room temperature through a stencil to the lead frame. The semiconductor device is urged against the adhesive to effect the attachment between the semiconductor device and the lead frame. The adhesive preferably is from about 75 percent to about 95 percent isobutyl acetal diphenol copolymer and from about 25 percent to about 5 percent, respectively, of titanium oxide.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 08/916,977,filed Aug. 14, 1997, now U.S. Pat. No. 5,840,598.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the manufacture of semiconductor deviceassemblies and, more particularly, to methods of assembly ofsemiconductor devices using room temperature adhesives and to theassembled semiconductor device and lead frame using room temperatureadhesives.

2. State of the Art

To manufacture a semiconductor device assembly, a semiconductor device,typically called a die or chip, is typically attached to a lead frame. Alead frame is a structure having a plurality of leads, bus bars, orother connecting structure to be electrically connected with thesemiconductor device. In a conventional lead frame, the lead frameincludes a die paddle to which the semiconductor device is attached anda plurality of leads extending inwardly to surround the periphery of asemiconductor device mounted on the die paddle. Subsequently, aplurality of wire bonds are made to connect the bond pads on the activesurface of the semiconductor device to the ends of the leads extendingaround the periphery of the semiconductor device. In a leads-over-chiptype lead frame (LOC lead frame), the lead frame is formed having no diepaddle and having a plurality of leads which extends over the activesurface of the semiconductor device being secured thereto to support thesemiconductor device, with a plurality of wire bonds being formedbetween the bond pads on the active surface of the semiconductor deviceand the ends of the leads of the lead frame.

A conventional lead frame or LOC frame may serve other functions. Thatis, it may assist in heat dissipation during manufacture, increase thestructural strength of the assembled semiconductor device as well asprovide convenient locations to make electrical connections.

In order to attach the semiconductor device to the lead frame, differentadhesives and adhesively coated tapes have been suggested. For example,U.S. Pat. No. 5,304,582 (Ogawa) shows use of adhesive tape withdifferent adhesives on opposite sides for attaching a die to a leadframe. U.S. Pat. No. 5,548,160 (Corbett et al.) discloses use ofadhesives including adhesives that have a core.

Typically, in attaching an LOC lead frame to a semiconductor device, adouble-coated adhesive tape is applied between the active surface of thesemiconductor device and the lead frame. The adhesive tape is typicallyan insulating carrier with a polymer adhesive on both sides tomechanically interconnect the lead frame and the semiconductor device.The tape composition and the amount of polymer adhesive used on the tapevaries with the size of the semiconductor device. It is desired to usethe least amount of adhesively coated tape to attach a semiconductordevice to a lead frame to attempt to minimize problems. Too much polymeradhesive added to the tape can cause a coefficient of thermal expansionmismatch between the lead frame, the polymer adhesive and thesemiconductor device which can contribute to the failure of the packageddevice. Reducing the size of the tape to enhance performance may involvereprocessing the tape at some increased cost and at some difficulty forthe smaller sizes. U.S. Pat. No. 5,548,160 (Corbett et al.)

If an adhesive, as opposed to an adhesively coated tape, is used toattach the semiconductor device to the lead frame, the quantity ofadhesive must be carefully controlled in the dispensing process. Thebond time for the adhesive is recognized to be difficult to control andcan vary greatly with variations in adhesive viscosity, adhesiveapplication temperature and amount of adhesive used. Further, adhesivecan bleed from under the lead finger and interfere with the attachmentof other lead fingers of the lead frame. Also, use of an adhesive (atelevated temperatures) may also lead to a nonuniform bond line betweenthe semiconductor device and the lead frame. That is, the semiconductordevice is not generally in alignment with the lead frame, causingdifferent spacings to be present between the lead fingers and the bondpads on the active surface of the semiconductor device, therebyaffecting wire bonding operations. Additionally, uneven application ofadhesive or non-uniform adhesive viscosity can lead to tilting of thesemiconductor device relative to the lead frame. An uneven or tiltedrelationship has been determined to be a factor that reducessemiconductor device assembly quality and leads to failures. U.S. Pat.No. 5,548,160 (Corbett et al.).

Therefore, an adhesive with better qualities suitable for direct bondingof the semiconductor device to the lead fingers of a lead frame isdesirable.

BRIEF SUMMARY OF THE INVENTION

A semiconductor device assembly is formed by joining a lead frame and asemiconductor device. The lead frame includes a plurality of leadfingers, each lead finger having a lower attaching surface for adhesiveattachment to portions of the active surface of a semiconductor device.

A non-conductive polymer adhesive is selected from the group ofadhesives that is tacky and compliant at room temperature, easilyapplied to a substrate, such as through the use of a stencil, and easilycured to a predetermined degree. The non-conductive polymer is applied,at room temperature, either to the lower surface of the lead fingers ofthe lead frame or to portions of the active surface of the semiconductordevice for compression therebetween. The lead fingers are connected bywire bonds to the bond pads on the active surface of the semiconductordevice.

The adhesive preferably has a first copolymer material selected from thegroup of copolymers that includes isobutyl compounds and a secondmaterial that is from a group of metal oxides that includes titaniumdioxide. Preferably, the first material is isobutyl acetal diphenolcopolymer. More preferably, the second material is titanium dioxide.

In a preferred composition, the adhesive has about 75 percent to about95 percent of isobutyl acetal diphenol copolymer and, respectively, fromabout 25 percent to about 5 percent of titanium dioxide.

Methods of assembling the semiconductor device assembly includeproviding a lead frame and a semiconductor device. A non-conductivepolymer adhesive is selected from the group that is tacky and compliantat room temperature and is applicable to a substrate through a stencil.The adhesive is applied to one of the semiconductor device and a surfaceof the lead frame at room temperature. The lead frame and thesemiconductor device are urged together at room temperature to attachthe semiconductor device to the lead frame and with electricalconnections between the lead fingers of the lead frame and the bond padson the active surface of the semiconductor device made by wire bondsextending therebetween.

In the preferred methods of assembly, the adhesive may be from thegroups of adhesives as described hereinbefore.

In an alternate configuration, a stencil is provided with the adhesive,at room temperature, applied to either a surface of each lead finger ofthe lead fingers or portions of the active surface of the semiconductordevice. The lead frame and the semiconductor device are thereafterpositioned relative to each other and urged together to effectattachment and electrical connection, if desired.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings which illustrate what are regarded as the best modes andpreferred embodiments for carrying out the invention:

FIG. 1 is a perspective simplified illustration of a semiconductordevice assembly of the invention;

FIG. 2 is a perspective simplified illustration of a semiconductordevice assembly of the invention with a stencil for applying adhesive;

FIG. 3 is a cross sectional depiction of portions of a semiconductordevice of the invention; and

FIG. 4 is a cross sectional depiction of portions of a semiconductordevice assembly of the invention with the semiconductor device and thelead frame in contact.

DETAILED DESCRIPTION OF THE INVENTION

Referring to drawing FIG. 1, a semiconductor device assembly 10 includesa lead frame 12 having a plurality of lead fingers 14 thereon. The leadframe 12 is one of a plurality that is connected in end-to-end fashion,thereby forming a strip or roll of lead frames. That is, lead frame 12is positioned between a preceding frame 16 and a following frame 18. Thelead frame 12 as well as the preceding frame 16 and following frame 18are driven or moved through a manufacturing environment by anappropriate drive or indexing system that engages the apertures 20formed in the opposite edges, or rails, 22 and 24. At a convenient time,the lead frames 12, 16 and 18 are separated one from the other and theopposite edges, or rails, 22 and 24 are removed so that each frame witha semiconductor device attached thereto becomes a separate and useablesemiconductor device assembly.

Each lead frame 12 is formed having a plurality of lead fingers 14, eachlead finger 14 having a lower surface, i.e., an undersurface orattaching surface 26. In some instances, the bond pads 36 of thesemiconductor device 34 may include bumps thereon to mate with each ofthe lead fingers 14 of the lead frame 12.

As illustrated in drawing FIG. 1, the semiconductor device 34 is anysuitable semiconductor device configured for attachment to the leadframe 12. The semiconductor device 34 has portions, bond pads 36, on theactive surface thereof configured for electrical connection to the leads14 of a lead frame 12. As illustrated, the semiconductor device 34 has aplurality of bond pads 36 thereon, all suitably positioned so that, uponproper positioning of the semiconductor device 34 with respect to theleads of a lead frame, the bond pads 36 are available for furtherconnection. The semiconductor device 34 may also have additional bondpads thereon.

Adhesive 40 is used to attach the lead frame 12 and the semiconductordevice 34 together. As shown in FIG. 1, the adhesive 40 may be appliedin a line or in a plurality of beads positioned for effecting attachmentof the semiconductor device 34 to the attaching surface 26 of the leadfingers 14 of the lead frame 12.

In operation, the adhesive 40 is preferably applied to an attachingsurface 26 of the lead fingers 14 of the lead frame 12. That is, theadhesive 40 is positioned on the attaching surface by any appropriatenozzle, roller, glue gun tip or the like. Upon urging the semiconductordevice 34 and the lead frame 12 together, the adhesive 40 is compressedand spread horizontally to effect an attachment. Since the adhesive ispreferably at room temperature, viscosity and flow is typically constantthroughout the adhesive. In turn, the risk of an uneven relationshipbetween the semiconductor device and the lead frame is reduced as thesemiconductor device and lead frame are assembled. Further, applicationat room temperature of the adhesive reduces heat induced failures in thesemiconductor device and lead frame assembly arising during the assemblyoperations.

As illustrated in drawing FIG. 2, the lead frame 60 is the same as leadframe 12. The lead frame 60 is positioned to pass relative to a stencil62. That is, a drive or indexing means (not shown) urges the lead frame60 as well as the preceding frame 64 and the following frame 66 to movepast the stencil 62. A source 67 of adhesive 68 is illustrated separatefrom the stencil 62 for clarity. In normal use, the stencil 62 ispositioned so that adhesive 68 from the source 67 is urged through theapertures 70 of the stencil 62 (by, for example, a piston) and onto theunderside or attachment surface 72 of the lead frame 60. The stencil 62may be configured with any desired pattern of apertures for depositionof adhesive 68 on an attaching surface 72 of the lead frame 60. Ofcourse, the adhesive may also be deposited on the active surface 73 ofthe semiconductor device 76.

The source 67 with stencil 62 and adhesive 68 may move up and downrelative to the attaching surface 72 to apply the adhesive 68 thereto.An anvil block 74 may be positioned opposite the stencil 62 so that thelead frames 60, 64 and 66 are all properly supported upon movement ofthe stencil 62 in close proximity and upon operation of the source 67 tourge the adhesive 68 outwardly to and in contact with the attachingsurface 72. A similar anvil block may be positioned so that the leadframe 60 is supported upon movement of the semiconductor device 76 intocontact with the adhesive on the attaching surface 72 of the lead frame60 and further upon compression of the adhesive 68 as the active surface73 of the semiconductor device 76 is urged toward the attaching surface72 of the lead frame 60. As the active surface 73 of the semiconductordevice 76 comes into contact with the attaching surface 72, bond pads78, 80 and 82 located on the active surface 73 of the semiconductordevice 76 are positioned to effect electrical connection withcorresponding lead fingers 60′ of the lead frame 60 as desired usingwire bonds.

Referring to drawing FIG. 3, a semiconductor device 34 is illustrated inrelation to the lead fingers 14 of a lead frame 12 having adhesive 40applied to the attaching surfaces 26 thereof.

Referring to drawing FIG. 4, a semiconductor device 34 is illustratedhaving the active surface 35 thereof secured to the attaching surfaces26 of the lead fingers 14 of a lead frame 12 (not shown) by the adhesive40 located therebetween. As previously stated, the adhesive 40 may beapplied to either the active surface 35 of the semiconductor device 34or the attaching surfaces 26 of the lead fingers 14 of a lead frame 12.The lead fingers 14 and the semiconductor device 34 are pressed intocontact with the adhesive 40, which is subsequently cured. Alsoillustrated, wire bonds 100 extend between and electrically connect thelead fingers 14 with the bond pads 36 on the active surface 35 of thesemiconductor device 34.

The adhesives 40 and 68 are non-conductive polymers selected from thatgroup or class of adhesives that is tacky and compliant at roomtemperature and is at the same time applicable at room temperature to asubstrate through a stencil such as stencil 70. The adhesives 40 and 68preferably have a first copolymer that is from the group of copolymersthat includes isobutyl compounds and is specifically isobutyl acetaldiphenol copolymer. The adhesive also contains a second material whichis from a group of metal oxides that includes titanium dioxide. Thepreferred adhesive has from about 75 percent by weight or volume toabout 95 percent by weight or volume of isobutyl acetal diphenolcopolymer and respectively from about 25 percent to about 5 percent byweight or volume of titanium dioxide. The amounts of the twoconstituents may vary somewhat from those stated so long as theresulting composition has the requisite tackiness and compliancy to besuitable to secure a semiconductor device and a lead frame at roomtemperature.

A suitable adhesive is available from International MicroelectronicsResearch Corporation of Nampa, Idaho under the product designationEXP/NCBP-4143-33 and is also known as NON-CONDUCTIVE BUMP POLYMER4243-33 (hereinafter referred to as the BUMP POLYMER). The BUMP POLYMERis particularly suitable because it may be applied at or near roomtemperature so that assembly can be effected at room temperature. Roomtemperature is generally deemed to be between 60° Fahrenheit (F.) and85° F. and may range from as low as 50° F. to as high as 95° F.

To manufacture the desired semiconductor devices, the user provides thenecessary lead frames in frame by frame sequence. Each lead frame has anattaching surface and connectors associated therewith. Semiconductordevices are also provided in a piece by piece sequence, each to beattached to an appropriate lead frame. Each semiconductor device hasbond pads thereon configured for electrical connection to the leadfingers of its respective lead frame.

A non-conductive polymer adhesive from the group that is tacky andcompliant at room temperature and is applicable through a stencil isselected and applied at room temperature to one of the semiconductordevice and the attaching surface of the lead frame and preferably theattaching surface. The semiconductor device and the attaching surfaceare urged together to effect a desired connection between the activesurface of the semiconductor device and the lead frame. Desirably, theadhesive selected is the isobutyl acetal diphenol copolymer withtitanium dioxide as hereinbefore described. In a preferred method, theadhesive is urged through the stencil as it is applied to the attachingsurface of the lead frame or the active surface of the semiconductordevice.

As previously stated, wire bonds are used to form the electricalconnections between the ends of the lead fingers of the lead frame andthe bond pads on the active surface of the semiconductor device.

Those skilled in the art will appreciate that modifications may be madeto the illustrated embodiment and the disclosed methods withoutdeparting from the spirit or principles of the invention and are notintended to limit the scope of the following claims.

What is claimed is:
 1. A method of attaching a semiconductor die to aportion of a lead frame, said method comprising: providing a lead framehaving a plurality of lead fingers thereon, at least one lead finger ofsaid plurality of lead fingers having an attaching surface; providing asemiconductor die having an active surface; selecting a non-conductivepolymer adhesive from a group that is tacky and compliant at roomtemperature; applying said non-conductive polymer adhesive in at leastone line on at least a portion said active surface of said semiconductordie; retaining said non-conductive polymer adhesive at room temperature;urging said active surface of said semiconductor die and said attachingsurface of said at least one lead finger of said plurality of leadfingers of said lead frame together at room temperature to attach saidsemiconductor die and said at least one lead finger of said plurality oflead fingers of said lead frame together connecting said attachingsurface of said at least one lead finger of said plurality of leadfingers of said lead frame and said active surface of said semiconductordevice.
 2. The method of claim 1, wherein a portion of saidnon-conductive polymer adhesive has a first copolymer material from thegroup of copolymers that includes isobutyl compounds.
 3. The method ofclaim 1, wherein a first portion of said non-conductive polymer adhesiveis isobutyl acetal diphenol copolymer.
 4. The method of claim 1, whereinsaid non-conductive polymer adhesive includes a first material from agroup of copolymers that includes isobutyl acetal diphenol copolymer anda second material that is from a group of metal oxides that includestitanium dioxide.
 5. The method of claim 4, wherein said non-conductivepolymer adhesive has from about 75 percent to about 95 percent by weightof isobutyl acetal diphenol copolymer and from about 25 percent to about5 percent by weight, respectively, of titanium dioxide.
 6. A method ofattaching a semiconductor die to a portion of a lead frame, said methodcomprising: providing a lead frame having an attaching surface;providing a semiconductor die having an attaching surface; selecting anon-conductive polymer adhesive which includes a first material from agroup of copolymers that includes isobutyl acetal diphenol copolymer anda second material that is from a group of metal oxides that includestitanium dioxide; applying said non-conductive polymer adhesive in atleast one line on at least a portion of said attaching surface of saidsemiconductor die; retaining said non-conductive polymer adhesive atroom temperature; and urging said attaching surface of saidsemiconductor die and said attaching surface of said lead frame togetherto attach said semiconductor die and said lead frame together connectingsaid attaching surface of said lead frame and said active surface ofsaid semiconductor die.
 7. A method of attaching a semiconductor die toa portion of a lead frame for use in a semiconductor device assembly,said method comprising: providing a lead frame having a plurality oflead fingers, each lead finger of said plurality of lead fingers havingan attaching surface; providing a semiconductor die having an attachingsurface; selecting an adhesive that includes from about 75 percent toabout 95 percent of isobutyl acetal diphenol copolymer and from about 25percent to about 5 percent, respectively, of titanium dioxide; applyingsaid adhesive in a line to at least a portion of said attaching surfaceof said semiconductor die; retaining said adhesive at room temperature;and urging said attaching surface of said semiconductor die and saidattaching surfaces of said plurality of lead fingers of said lead frametogether at room temperature to attach said semiconductor die and saidlead frame together connecting said attaching surfaces of said leadfingers of said plurality of lead fingers of said lead frame and saidportions of active surface of said semiconductor die.
 8. A method ofattaching a semiconductor die to a portion of a lead frame for use in asemiconductor device assembly, said method comprising: providing a leadframe having at least one attaching surface; providing a semiconductordevice having an attaching surface; providing a stencil having a patterntherein; selecting a non-conductive polymer adhesive from a group thatis tacky and compliant at room temperature and is applicable to asubstrate through a stencil; positioning said stencil and said attachingsurface of said semiconductor device relative to each other; applyingsaid non-conductive polymer adhesive in at least one line to a portionof said attaching surface of said semiconductor device through saidstencil; retaining said non-conductive polymer adhesive at roomtemperature; positioning said at least one attaching surface of saidlead frame and said attaching surface of said semiconductor devicerelative to each other; and urging said attaching surface of saidsemiconductor device and said at least one attaching surface of saidlead frame together to attach said semiconductor device and said leadframe together.
 9. A method of attaching a semiconductor die to aportion of a lead frame for use in a semiconductor device assembly, saidmethod comprising: providing a lead frame having at least one attachingsurface; providing a semiconductor device having an attaching surface;providing a stencil having a pattern therein; selecting a non-conductivepolymer adhesive which includes a first material from a group ofcopolymers that includes isobutyl acetal diphenol copolymer and a secondmaterial that is from a group of metal oxides that includes titaniumdioxide; positioning said stencil and said attaching surface of saidsemiconductor device relative to each other; applying saidnon-conductive polymer adhesive in at least one line through saidstencil to at least a portion of said attaching surface of saidsemiconductor device; retaining said non-conductive polymer adhesive atroom temperature; positioning said at least one attaching surface ofsaid lead frame and said attaching surface of said semiconductor devicerelative to each other; and urging said attaching surface of saidsemiconductor device and said attaching surface of said lead frametogether at room temperature to attach said semiconductor device andsaid lead frame together.
 10. A method of attaching a semiconductor dieto a portion of a lead frame for use in a semiconductor device assembly,said method comprising: providing a lead frame having at least oneattaching surface; providing a semiconductor device having an attachingsurface; providing a stencil having a pattern therein; selecting anadhesive including from about 75 percent to about 95 percent of isobutylacetal diphenol copolymer and from about 25 percent to about 5 percent,respectively, of titanium dioxide; positioning said stencil and saidsemiconductor device relative to each other; applying said adhesivethrough said stencil in at least one line to said attaching surface ofsaid semiconductor device; retaining said adhesive at room temperature;positioning said lead frame and said semiconductor device relative toeach other; and urging said semiconductor device and said lead frametogether to attach said semiconductor device and said lead frame usingsaid adhesive.